Performance improvements when rendering

- Fast path for JSON, XML and plain text rendering

render/text.go

@@ -0,0 +1,25 @@
+package render
+
+import (
+	"fmt"
+	"net/http"
+)
+
+type plainTextRender struct{}
+
+func (_ plainTextRender) Render(w http.ResponseWriter, code int, data ...interface{}) error {
+	format := data[0].(string)
+	values := data[1].([]interface{})
+	WritePlainText(w, code, format, values)
+	return nil
+}
+
+func WritePlainText(w http.ResponseWriter, code int, format string, values []interface{}) {
+	WriteHeader(w, code, "text/plain")
+	// we assume w.Write can not fail, is that right?
+	if len(values) > 0 {
+		fmt.Fprintf(w, format, values...)
+	} else {
+		w.Write([]byte(format))
+	}
+}